The present invention relates to a fail-safe control system for a four wheel steer system for steering rear wheels together with front wheels.
Japanese patent provisional publication No. 59-128054 discloses one conventional example of such a fail-safe control system. The system is arranged to fix the rear wheels in a straight ahead position in order to ensure the vehicle stability when a failure is detected in a control system for controlling the rear wheel steer angle. However, this sytem damages the stability in the high vehicle speed range when the vehicle is designed to gain a sensitive steering response in the low and medium speed range and to secure the vehicle stability in the high vehicle speed range by steering the rear wheels in the same direction as the front wheels.